JP-2002-175744A shows a conventional range detector for a vehicular automatic transmission. In such a range detector, a movable member slides on sliding surface of a guide member according to a selected rage of the automatic transmission. A range detector detects the position of the movable member to identify the range of the automatic transmission.
When the movable member is positioned in the same position for a long period, dust particles are adhered on the siding surface of the guide member. Particularly, in the range detector positioned in the automatic transmission as shown in JP-2002-175744A, since the operation fluid flows around the movable member, metal particles produced by abrasions of friction elements and gears and contained in the operation fluid tend to be adhered on the sliding surface of the guide member. Such a particles are introduced between the movable member and the sliding surface, which may generate a large sliding resistance. In this case, the movable member hardly moves smoothly, and the sliding member, the guide member, and the detector may be failed, which causes a malfunction of the range detector.